Identification of bacterial contamination in food often occurs subsequent to an outbreak of a foodborne illness. The bacterium Escherichia coli is frequently identified as the food contaminant of many foodborne illnesses. The serotype known as E. coli O157:H7 causes enterohemorrhagic colitis and possibly kidney failure. It often results in hospitalization of the infected patient and can be particularly lethal in young children and the elderly. O157:H7 is most often associated with outbreaks of foodborne illness in the United States and elsewhere in the world.
Detection of pathogenic E. coli, particularly serotypes causative of hemorrhagic colitis has become a public health priority. O157:H7 is frequently isolated from cattle, including healthy animals and has also been associated with illness in contaminated produce. The presence of O157:H7 in a food product released to consumers is considered as evidence of adulteration of the product. Regulations by the United States government require meat processors to screen for the presence of O157:H7 in their finished products and more stringent guidelines are being considered in a number of states for the identification of O157:H7 in other commodities and food stuffs. An assay for the rapid, sensitive and specific detection of infectious pathogens is extremely important from both a public health and economic perspective.
Many strains of genetically similar E. coli exist that vary dramatically in their pathogenicity. Genomic comparisons are revealing the consequences of genetic changes often underlie the emergence of new pathogenic bacteria. E. coli O157:H7 has been determined to have evolved stepwise from the O55:H7 which is associated with infantile diarrhea. These two serotypes are more closely related at the nucleotide level while divergence was markedly different at the gene level. Likewise, other pathogenic serotypes have been shown to be less divergent at the nucleotide level making identification of pathogenic strains difficult.
An assay utilizing molecular methods such as sequence specific amplification and detection offer significant improvements in speed, sensitivity and specificity over traditional microbiological methods. Design and development of a molecular detection assay that requires the identification of a target sequence that is present in all organisms to be detected and absent or divergent in organisms not to be detected is an unmet need for the definitive detection of the O157:H7 serotype of E. coli. 